1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to multi-piece golf balls having a center, a mid layer and a cover.
2. Description of the Related Art
Golf players' greatest demand for golf balls is flight performance. Golf players emphasize flight performance with a driver, a long iron and a middle iron. The flight performance is correlated with spin rate. The golf ball flies at a small spin rate, thereby obtaining proper trajectory to accomplish great flight distance. In light of flight performance, golf balls which are not likely to be spun are desired.
When a golf ball has an outer-hard/inner-soft structure, the spin may be suppressed. The conventional golf ball uses a soft center, a hard mid layer and a hard cover in order to attain an outer-hard/inner-soft structure. In this golf ball, the hardness distribution up to the central point of a center from the surface of a mid layer has a large level difference on the boundary of the center and the mid layer. This level difference deteriorates the suppression of spin.
When an inertia moment is set to be large, the spin may be suppressed. A golf ball having a hollow structure may attain a large inertia moment. A variety of golf balls having the hollow structure have been proposed. Japanese Unexamined Utility Model Application Publication No. 3-63354 discloses a golf ball which is made of a hard rubber or a hard plastic, and has a spherical body encapsulating high-pressure air therein. Japanese Unexamined Patent Application Publication No. 11-76464 discloses a golf ball having a hollow center. Japanese Unexamined Patent Application Publication No. 11-128399 (U.S. Pat. No. 6,182,970) discloses a golf ball having a hollow core.
According to the golf ball disclosed in Japanese Unexamined Utility Model Application Publication No. 3-63354, a layer covering a space portion is hard. The space portion has a hardness of zero. In this golf ball, a hardness difference between the space portion and the portion covering the space portion is large. When this golf ball is hit, the portion covering the space portion is deformed significantly. Since the portion covering the space portion has small recoil, excessive spin is caused.
According to the golf ball disclosed in Japanese Unexamined Patent Application Publication No. 11-76464, a rubber layer of the center is hard. This golf ball has a large hardness difference between the space portion and the rubber layer. When the golf ball is hit, the rubber layer is deformed significantly. Since the rubber layer has small recoil, excessive spin is caused.
According to the golf ball disclosed in Japanese Unexamined Patent Application Publication No. 11-128399, a rubber layer of a core is hard. This golf ball has a large hardness difference between the space portion and the rubber layer. When the golf ball is hit, the rubber portion is deformed significantly. Since the rubber layer has small recoil, excessive spin is caused.
It is an object of the present invention to provide a golf ball having great flight distance by suppressing the spin.